Extremely agreed. I wanted to make a SCARA arm and it would basically be impossible without a printer. Basically, you can't make something efficiently if you don't know how the fabrication technique works and what its strengths and weaknesses are.
For another example, I made this case:
https://www.makerfol.io/project/8ycrZ9t-case-for-the-dp30v5a...
This would also have not been possible without the printer next to me. I constantly had to print segments to see how parts fit. With a week-long turnaround time instead of ten minutes, I wouldn't even have bothered.
Sure, if I already know how to design and print, maybe I could have designed something without owning a printer, but even that is not very likely (I generally have to make alterations a lot). For $300 (and a bunch of time spent), it's a no-brainer if you want to get into the hobby.